diff --git a/packages/docusaurus-preset-classic/src/index.ts b/packages/docusaurus-preset-classic/src/index.ts
index 66a3312110..b88be1f9b8 100644
--- a/packages/docusaurus-preset-classic/src/index.ts
+++ b/packages/docusaurus-preset-classic/src/index.ts
@@ -29,7 +29,11 @@ export default function preset(
 ): Preset {
   const {siteConfig} = context;
   const {themeConfig} = siteConfig;
-  const {algolia, googleAnalytics, gtag} = themeConfig as ThemeConfig;
+  const {
+    algolia,
+    googleAnalytics,
+    gtag,
+  } = (themeConfig as unknown) as ThemeConfig;
   const isProd = process.env.NODE_ENV === 'production';
 
   const themes: PluginConfig[] = [];